[Python-Dev] PySet API (original) (raw)

Raymond Hettinger raymond.hettinger at verizon.net
Sun Mar 26 18:43:35 CEST 2006

[Aahz]

Speaking as a person who does relatively little C programming, I don't see much difference between them. The first example is more Pythonic -- for Python. I agree with Barry that it's not much of a virtue for C code.

It was a trick question. Everyone is supposed to be attracted to the _next version because it is shorter, faster, and takes less ref counting management. However, the _next version has a hard-to-find bug. The call to PyObject_Hash() can trigger arbitrary Python code and possibly mutate the table, leaving pointers to invalid memory addresses. It would likely take Armin less than five minutes to write a pure Python crasher for the code. And THAT is why PySet_Next() should never come into being.

The iterator form is more duck-typable and re-usable than the set specific _next version, but the example was chosen to take that issue off of the table and just focus on mutation issues.

However, I do have one nitpick with both your examples; I don't know whether this is an artifact of them being examples:

hash ^= h * 3644798167; Seems to me that magic numbers like this need to be made constants and explained with a comment

FWIW, the actual code does have comments. I stripped them out of the posting because they weren't relevant to the code comparison.

Raymond

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